1. The SPD geometry in AliRoot Alberto Pulvirenti University & INFN Catania In collaboration with: Domenico Elia (INFN Bari) Outline:  Implementation  Volumes & Displacement  Material budget estimates  Cables and sevices on the cones  Outlook 3° Convegno Nazionale sulla Fisica di ALICE Frascati – LNF, 14 November 2007

2. 2 Advantages of ROOT geometry modeling  Modeler independent from transport code (GEANT3, FLUKA, …) › geometry is implemented once for all transport engines › easy to be interfaced with the virtual “generic” simulation engine (TVirtualMC) › easy to swtich among different transport codes  Geometry built with ROOT classes › reusability for reconstruction › easy to implement (mis)alignment of modules

3. 3 Components of a TGeo geometry  [TGeo]Medium: › a tracking medium (material + physical status)  [TGeo]Volume: › a block of material, which represents a part of the detector › a box which contains several sub-volumes, in order to be able to replicate a composite structure made of several parts  [TGeo]VolumeAssembly: › a “virtual” space with several volumes inside useful to manage situations where a group of volumes can superimpose on another group of volumes

4. 4 Implementation philosophy  Multi-level implementation: › all groups of volumes which are replicated many times in the whole detector are inserted into an “upper level” container …which will be a TGeoVolume or TGeoVolumeAssembly depending on how its components are displaced in space  Advantages: › reduces the elements to be checked in case that corrections are needed › “logic” of the implementation is more easily readable and followable

5. 5 Half-stave architecture Aluminum-polyimide grounding foil (25 + 50 µm thick) with 11 windows to improve the thermal coupling Multi-chip module (MCM) to configure and read-out the half-stave 2 Ladders consisting of: p+n silicon sensor matrix 200 µm thick with 40960 pixels arranged in 256 rows and 160 columns 5 FE chip Flip-chip bonded to the sensor through Sn-Pb bumps [single cell dimensions = 50 µm (r  ) x 425 µm (z)] Aluminum-polyimide multi-layer bus to connect the MCM and FE chip

6. 6 HALF STAVE “BASE” MCM “Extenders” Grounding Foil Ladder Uppermost level Implemented as an assembly, to avoid some overlaps on the sector. ‘Box’ volume containing the grounding foil and the ladders. Thin cables which go from inside to outside the sensitive area of the SPD. MCM Cover Chips inside MCM Pixel Bus Extender Sensor Chips Kapton Al MCM Extender Implementation levels Bumps Glues Grease Alignable Volumes MCM base Pixel Bus “Base” Pt1000 Resistors Capacitors

7. 7 Stave architecture  1 Stave = 1 “left” half-stave + 1 “right” half-stave “LEFT”-type half-stave “RIGHT”-type half-stave Example: couple of half-staves on the outer layer A - side C - side z x

8. 8 Ladder  = 1 sensor + 5 chips + 32 bump-bondings  one single container bump bondings implemented in “stripes” (1 x column) ‏ of - 0.042 mm width - 0.013 mm thickness guard ring around the sensor

9. 9 Grounding foil  Complicated shape with holes inside › holes are filled with thermal grease  Cosisting in two layers (kapton & aluminum) › Small differences in size

10. Big resistors and capacitors in correspondence of the end of each ladder Pt1000’s (one per chip) Pixel bus

11. 11 Half-stave assembly Glue CARBON FIBER SUPPORT Grounding Foil Glue Ladder Glue Pixel Bus Needed some room for movement of ladders and half-staves to implement misalignment: this could cause an overlap of volumes. SOLUTION: reduce glue layer thickness to leave some “free space” around the ladder and between GF and support, without changing the spacing between components Glue

12. 12 Pixel bus & extenders (by R. Vernet)  Implemented as “folded” foils  Volumes must intrude in each other  TGeoVolumeAssembly

13. 13 MCM  Thin integrated circuit + Chips + Thick cover

14. 14 Clips  Component on 3 over the 4 staves lying on layer 2

15. 15 Placement on sector  Use reference points in the support placement planes

16. 16 Final appearance

17. 17 Tests (1) what is done on the way along implementation  Fix coding conventions › usually done before committing on CVS (by me or Massimo Masera)  Remove overlaps › the volumes must not overlap with each other, because this can cause the transport of particles to get confused and return meaningless data › a ROOT facility allows to check overlaps by sampling: 1.points are generated randomly in the volume of the complete geometry 2.for each point it is checked if it belongs to more than 1 volume 3.an alert is raised when this happens  an overlap is present somewhere  Event generation in AliRoot with new geometry › check execution CPU time to detect anomalous increases due to slow geometry creation (e.g. due to a too large amount of volumes) › make sure that no run-time errors are raised

18. 18 Tests (2) what will be done with dedicated tests  Check materials used for implementation › for objects present in the old geometry: translate their definition in TGeo language (done by Ludovic Gaudichet) › for new objects only present in new geometry when possible, reuse old definition (chips, silicon, …) when not possible, a dedicated study is required to define new materials  Radiation Length maps › comparison between “old” and “new” geometries › comparison with computations from technical details

19. 19 Calculated material budget (as implemented) 1.090 1.197 0.530 INNER LAYER OUTER LAYER TH. SHIELD

20. 20 Cables and services on the cones: what is there

21. 21 Summary & outlook  The new TGeo package allows a definition of a detector geometry decoupled from transport code › ease switching among different transport codes › ease interacting with geometry also in reconstruction  Implementation of SPD has started since several months › Implemented part is almost equivalent to the actual geometry › work started for implementation of other components on cones  Testing of new geometry on the way › Preliminary tests being done for radiation length maps and event generation › Test on materials is going to start

22. 22

23. 23 X 0 map: comparison with old geometry (very preliminary result) with “geantinos” Z (cm) Φ (deg) Z (cm) New Old Layer 2 R = 6.5  7.5 cm

24. 24 X 0 map: comparison with old geometry (very preliminary result) with “geantinos”: difference Z (cm) Φ (deg) Layer 2 R = 6.5  7.5 cm

25. 25 Cables and services on the cones: some estimates 1. Extenders: 12 per each (half-)sector: - 6 x pixel-bus - 6 x MCM 18 o 54 o 90 o 126 o 162 o X/Xo = 6*(0.11/285.7+0.14/14.3) = 6% X/Xo = 6*(0.10/285.7+0.10/14.3) = 4.4%

26. 26 Cables and services on the cones: some estimates 2. Optical patch-panels 10 in total, 1 per each (half-)sector 18 o 162 o 115 o 90 o 62 o 100mm 50mm xy yz 4mm Aluminium X/Xo = 4/27.0 = 14.8%

27. 27 Cables and services on the cones: some estimates 3. Plates holding the extenders 10 in total, 1 per each (half-)sector at  middle of the cone 50mm 5mm xy 30mm 2mm Carbon fiber xz 50mm 200mm X/Xo = 5/223.5 = 2.2%

28. 28 Cables and services on the cones: some estimates 4. Tubes for detector cooling Flexible parts: 6mm 1mm Inox Central (rigid) part: may be assumed with same diameter but thinner walls (0.3mm) X/Xo = 2/17.2 = 11.6%

29. 29 Cables and services on the cones: some estimates 5. Other materials 4 of these capillars on the cone PHYNOX ducts 2.6mm xternal diameter 0.040mm thick walls X/X0 = 0.080/16.1 = 0.5% CARBON FIBER holding plate 300mm x 30mm 0.3mm thick X/X0 = 0.3/223.5 = 0.1% Cu/Ni (30/70) ducts 1.85mm external diameter 0.35mm thick walls 200mm length X/X0 = 0.7/14.3 = 4.9% Optical fibers (quartz) 18 per halh-sector: 9/125/900  m buffered fibers 1 fiber: X/X0 = 0.9/100 = 1.6% 18 fiber pockets  4.5mm X/Xo = 4.5/100 = 4.5%